Tight racking challenges
December 1st 2009

Squeezing the highest number of racking runs into any given storage cube may adversely affect the efficiency and productivity of forklift fleets says John Maguire, sales and marketing director of Narrow Aisle Flexi

With warehouse and distribution centre managers under constant pressure to make maximum use of all available storage space within their facilities, it is seen to be essential that the width of the aisles along which materials handling equipment and order picking staff travel around the store is kept to an absolute minimum.

Traditionally, the narrowest aisle widths were achieved by using guided VNA forklifts.VNA machines can - depending on load sizes - work in aisles as narrow as 1.6 metres because they turn only the load while other forklifts turn the entire vehicle in the aisle.

As a result, modern warehouse designers and some forklift truck manufacturers now place too much emphasis on achieving the narrowest aisleways and, in some cases, safety and productivity can be compromised.

Although I would be the first to acknowledge that the accepted wisdom when it comes to restricting aisle widths has certainly benefited articulated forklift truck sales, narrowing the aisles has become something of an obsession.

By attempting to squeeze the highest number of racking runs into a storage cube many companies are in danger of adversely affecting the efficiency and productivity of their forklift fleet.

Quite simply, narrowing the aisleways too much restricts the speeds at which a forklift can travel between picking locations.

When using an articulated forklift truck it is technically feasible to pick up and turn pallets in aisles as narrow as 1.6 metres, but in applications where high throughputs need to be achieved, faster travel speeds are required. If there is insufficient clearance in the aisleway, then the speed at which the truck can be safely operated will be reduced.

The two most important dimensions when assessing the ideal aisle width for any fast moving operation involving articulated trucks is first the distance diagonally across the pallet, ie, from one corner to another when a pallet is being rotated in the aisle.

The safety clearance of 100mm either side (200mm in total) of a typical pallet will need to be added to ensure fast pallet put-away and retrieval. The second dimension is the overall width of the truck chassis when travelling along the stacking aisle.

Furthermore, because everyone – particularly retailers – wants less inventory in store so the amount of break-bulk and ground level picking of single items is growing fast and this means that the safety of order pickers working in the aisles at the same time as trucks is likely to become an increasingly central safety issue.

From the feedback we have had from warehouse operators, there is growing concern that the use of traditional guided products such as Man-Up VNA Combis can compromise health and safety and order picking efficiency within warehouses where customers have had to move to faster low order picking for efficiency and cost reasons.

In fact, these days it is widely accepted that there are significant drawbacks to having a man order picking some way above the ground. For example, because man-up Combi VNA trucks are physically big pieces of kit, storage schemes have to incorporate large transfer gangways at both ends of each aisle to allow these long trucks to switch aisles. This often means that the space savings achieved by the man-up machine's ability to operate in impressively very narrow aisles can be lost.

Furthermore, there are safety issues. A man-up Combi VNA truck operator who is working 10 metres in the air, will often struggle to notice another order picker working at ground level in the same aisle - thereby compromising order picking efficiency and health and safety within sites where there is a high degree of low level order picking.

In short, what had - in the early days of the Man-Up VNA Combi truck - been seen as the truck's key advantages, are now considered handicaps by many logistics experts.

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